U.S. Pat. No. 4,611,839, issued Sept. 16, 1986, teaches a rigid pipe coupling in which the respective coupling segments each are provided with an end face at the respective opposite ends of the coupling segments, the respective end faces being oppositely inclined with respect to an X, Z plane of that coupling segment.
The provision of those oppositely inclined end faces permits rotation of the respective coupling segments about a Y--Y axis during tightening down of the coupling to bring keys of the respective coupling segments into clamping engagement either with side walls of a groove formed in the end of the associated pipe, or, the axial wall of that groove, or both, and in turn permits the internal circumferential length of a coupling assembled from those coupling segments to decrease during tightening down of the coupling.
The extent of rotational movement of the respective coupling segments is determined by engagement of the keys with the side walls of the pipe grooves, or, by the slope of the end faces in the X, Z plane, and, the extent to which the coupling segments move radially of the pipe axis before reaching clamping engagement with the pipe end.
This, in turn, can result in the X,Y plane of the respective coupling segments being oriented at an angle to the X,Y plane of the pipe i.e. in a staggered and axially non-aligned orientation of the coupling segments as related to the longitudinal axis of the pipe.
While this poses no problems in conventional uses of such segmented pipe couplings, and in fact constitutes a substantial advantage of such segmented pipe couplings, it poses a particular problem in situations in which the respective coupling segments are required to remain with their respective X,Y planes within a determined angle of divergence from the X,Y plane of the pipe.